Ethylnitrosourea (ENU) is a powerful transplacental carcinogen. A single dose to a pregnant rat produces central and peripheral nervous system tumors in the adult offspring many months after birth. These tumors, routinely produced in our department, are available for use in cytogenetic and cell culture studies. We have shown that tumorigenic doses of ENU produce chromosome aberrations in cultured cells and in bone marrow of treated animals. These studies have also been extended to brain and liver tissue of fetuses, where chromosome aberrations can also be demonstrated 4-8 hours after administration of ENU to the mother. These studies suggest that a mutation could be an indicator of and, possibly, an explanation for the oncogenic effect. Our preliminary evidence indicates that trisomy 4 is a consistent chromosome finding in neurogenic tumors induced by ENU in the rat. The chromosome abnormality is found in cell cultures of primary tumors, after agar cloning of tumor cells and after several cycles of passage from cell culture to animal. Information on other tumors will be collected to determine whether this is a consistent finding in other tumors of the nervous system as well as for the trigeminal nerve. A "marker" chromosome could be used to investigate the oncogenic process. We propose to study early changes in trigeminal nerve tumors. Trigeminal nerve roots will be removed from young rats treated with ENU transplacentally, and initiated in cell culture. At various stages, cells will be examined for oncogenic transformation and cytogenetic changes and injected into newborn hosts to test for tumorigenicity.